pvc

I'm by no means an expert but this is my understanding. The PCV should have a hose going to the flame arrestor. When air is being pull through the carb, it will also pull air through that hose, through the valve and from the crankcase. The idea is any volitile hydrocarbons will be sucked into the carb and burned by the engine. The way I've always undersood to tell if it's bad is to pull it out of the crankcase with the engine running and stick your finger over the hole. If it sucks it's ok. I've also heard you completely disconnect it and shake it. You should hear the valve rattle around. If the valve doesn't move freely, replace it. That's my understanding. Maybe somebody that knows what they're talking about can chime in.

PCV hose connects to the carb PCV fitting or the PCV plate under the carb.

The breather hose goes to the flame arrestor and allows air to enter the engine to equalize pressures in the engine circulating internaly though the engine to the PCV valve.

I think y'all are right. On my Commandar engine, there are two hoses that go to the spark arrestor but now that I think about it, neither are for the PCV. One is attached to the valve cover breather and I can't remember where the other attaches. I'd check but I'm 200 hundred miles from home. But...this brings up another concdern on my part...my breather doesn't fit snugly on the valve cover. Is this a problem? should there be a gasket or something that should make it fit tighter? It's pretty loose.

Holley's have a screw on the bottom of the baseplate that you can screw in ever so slightly to crack open your secondaries that will help engines with a rough idle. Depending on whether the secondaries are cracked or not cracked could be the problem.

Look for a vaccuum leak around the base of the carb or where the intake and heads meet. Take a can of carb cleaner, brake cleaner or even propane and spray around the base of the carb and listen for the RPM to pick up a little if it does then you have found the leak. Also double check the timing and maybe even give it two degrees more of advance of base timing.

As well as keeping the crankcase moisture free, I believe the main purpose of the PVC valve is to reduce engine emissions. The "blow by" in the crankcase gets returned back into the intake instead of going in the air. Some old GM Engines like our OMC 225 in the 74 Mustang has crankcase vents on each valve cover with NO PCV vales-just a elbow that looks like one. They go to the flame arrestor (no manifold vacuum-not as effective).

Ok, I guess I will chime in.

Gordon:

Yes, the exhausts can get plugged. It is not uncommon for old rubber exhaust hose to collapse internally and significantly block the exhaust. Some say this is by design to snuff out an overheated engine before damage is done...I dunno, doubt it. But anyway, they can and do collapse internally. Usually you would notice this as loss of power but not necessarily idle quality...but who knows.

As far as PCV, my take is that you should temporarily disconnect this and plug the port at the carb to ensure this is not the cause of your idle problem. Many auto engines of old had the PCV plumbed to the air cleaner (i.e. spark arrestor on boats). The main purpose of the PCV is to allow blow-by gases to escape the engine thereby avoiding built up pressure that would cause seals to leak. And to allow unburned fuel and moisture a path out of the engine via evaporation.

IF the carb is as perfect as you say it is (I would borrow another carb to test), then I agree with 70nautique and I would play around with the timing. Forget the specified setting and set it by ear. Advance the timing until you achieve the highest rpm AND smoothest idle. Then back it off slightly to avoid pre-ignition. Test it under load. If it pings, then back it off slightly more.

Good luck.